The present invention relates generally to semiconductor fabrication, and more particularly to methods for fabricating improved ultra-large scale integration (ULSI) semiconductor devices such as ULSI metal oxide silicon field effect transistors (MOSFETs).
Semiconductor chips are used in many applications, including as processor chips for computers, and as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices that use semiconductor chips advantageously is minimized, while nevertheless improving the memory capacity and computing power of the devices.
One general method for making semiconductor chips is referred to as the xe2x80x9cbulkxe2x80x9d CMOS method, wherein well implants are formed in a bulk silicon substrate to promote subsequent proper functioning of the chip, and then transistor stacks are formed on the substrate. A newer chip making method referred to as xe2x80x9csilicon on insulatorxe2x80x9d or xe2x80x9cSOIxe2x80x9d has also been introduced which does not require the formation of wells in the substrate, and which provides for faster transistor switching speed, improved resistance to soft error and latch-up, and higher transistor density. Moreover, SOI chips advantageously consume less power when inactive compared to bulk CMOS chips.
As recognized by the present invention, however, the SOI process implicates complications, including the implantation of high doses of oxygen into the substrate. As understood herein, the high dose of oxygen that is required can lead to a relatively high defect rate in the SOI film, consequently requiring high temperature annealing for prolonged periods to alleviate the defects. Unfortunately, this in turn makes it difficult to precisely control the SOI film thickness, which is undesirable because a uniform SOI film thickness promotes optimal chip functioning. Also, because of the prolonged annealing, manufacturing throughput is lower than might be desired. Fortunately, the present invention has recognized the above problems and has provided the solutions herein.
A method is disclosed for forming a silicon on insulator (SOI) device. The method includes depositing an amorphous silicon film on a substrate, and establishing protective stacks in the film. Active region windows are established over first regions of the film between protective stacks. Laser energy is then directed through the active region windows against the first regions to anneal the first regions. As disclosed further below, the first regions establish active SOI regions after annealing and cooling.
In one preferred embodiment, the protective stacks are made of an oxide. On the other hand, the substrate is made of a material selected from a group consisting essentially of: sapphire, silicon oxide, and silicon nitride.
The preferred method of establishing the active region windows includes masking the first regions of the film to establish stack windows over second regions of the film. The second regions of the film are then removed, and an oxide material is deposited to fill the stack windows. Next, the first regions are unmasked to establish the active region windows, prior to laser annealing.
In another aspect, an SOI semiconductor device includes a substrate and active regions of recrystallized silicon on the substrate disposed between inactive regions of oxide.
In yet another aspect, a method for making an SOI device includes providing a substrate, and depositing an amorphous silicon film on the substrate. Moreover, the method includes masking intended active regions of the film. Also, the method contemplates removing unmasked regions of the film to establish stack windows, and then depositing an oxide in the stack windows. The intended active regions are unmasked and activated using laser annealing followed by cooling.
In a preferred embodiment, the method includes heating the intended active regions to at least nine hundred degrees Celsius (900xc2x0 C.). Indeed, the intended active regions can be heated to at least nine hundred fifty degrees Celsius (950xc2x0 C.). Preferably, the activating act is accomplished by pulsing a laser beam against the intended active regions to melt the regions.
Other features of the present invention are disclosed or apparent in the section entitled xe2x80x9cDETAILED DESCRIPTION OF THE INVENTION.xe2x80x9d